HR: 17:20h
AN: U14A-05    [Abstracts]
TI: A new Application of Ar-40/Ar-39 Dating: A Provenance Study of Middle Stone Age Obsidian Tools from Ethiopia
AU: * Nomade, S
EM: snomade@bgc.org
AF: Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709 United States
AU: * Nomade, S
EM: snomade@bgc.org
AF: Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA 94720 United States
AU: Vogel, N
EM: nvogel@bgc.org
AF: Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709 United States
AU: Vogel, N
EM: nvogel@bgc.org
AF: Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA 94720 United States
AU: Renne, P R
EM: prenne@bgc.org
AF: Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709 United States
AU: Renne, P R
EM: prenne@bgc.org
AF: Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA 94720 United States
AU: Negash, A
EM: agazi@uclink.berkeley.edu
AF: Laboratory for Human Evolutionary Studies, University of California Berkeley, Berkeley, CA 94720 United States
AB: The identification and geographic origin of potential sources for obsidian tools manufactured by MSA (Middle Stone Age) hominid groups is important to reconstruct source utilization and trade routes. Obsidian sourcing is done by geochemical investigation of obsidian artifacts and potential source materials and the identification of possible matches between them [e.g., 1]. Due to uncertainties arising, e.g., from intrasource inhomogeneities [2] additional methods are desirable. As a part of a pilot study, we dated by Ar-40/Ar-39 stepwise heating numerous debitage pieces of obsidian artifacts from an MSA excavation site and several potential source rock samples from a nearby obsidian outcrop in the Gademotta-Kulkuletti area near Ziway lake, Ethiopia. The ages were used, along with chemical data, to trace possible source rocks used to manufacture the artifacts. Most of the debitage samples show ages around 1.29 Ma and exhibit flat, well behaved spectra. Less well behaved spectra are obtained for two debitage samples with ages of about 1.26 Ma, and two with ages of about 0.62 Ma. We point out that despite this significant spread in the ages found, all debitage samples as well as the potential source rocks show homogeneous major and trace elemental compositions generally indicating a positive match in archeological sourcing. The ages of two potential source rocks are about 1.26 and 0.87 Ma. Thus, while there is a match with the two debitage pieces dated at 1.26 Ma, the exact outcrop of the major source for the 1.29 Ma old artifacts has not been identified yet. A second set of samples with further possible source materials for the Kulkuletti artifacts as well as another potential debitage-source material pair from a second excavation site in the Ziway lake area, Porc Epic, are currently being dated and will be presented at the conference. Already this first set of data shows not only the general applicability of Ar-40/Ar-39 dating to archeological obsidian sourcing, but also its great potential as a complementary tool revealing more detailed information than the geochemical data alone. [1] Merrick and Brown (1984) African Archaeological Review 2:129-152. [2] Shackley (1998) Journal of Archaeological Science 25: 1073-1082.
DE: 9305 Africa
DE: 9604 Cenozoic
DE: 1035 Geochronology
SC: Union [U]
MN: 2004 AGU Fall Meeting